Latest on Fukushima from the NYTimes.
Richard T. Lahey Jr., who was General ElectricÂs chief of safety research for boiling-water reactors when the company installed them at the Fukushima Daiichi plant, said that as seawater was pumped into the reactors and boiled away, it left more and more salt behind.
He estimates that 57,000 pounds of salt have accumulated in Reactor No. 1 and 99,000 pounds apiece in Reactors No. 2 and 3, which are larger.
The big question is how much of that salt is still mixed with water and how much now forms a crust on the reactors uranium fuel rods. Chemical crusts on uranium fuel rods have been a problem for years at nuclear plants.
Crusts insulate the rods from the water and allow them to heat up. If the crusts are thick enough, they can block water from circulating between the fuel rods at all. As the rods heat up, their zirconium cladding can ignite, which may cause the uranium inside to melt and release radioactive material.
[...]
Preventing the reactors and storage pools from overheating through radioactive decay would go a long way toward limiting radioactive contamination. But that would require pumping a lot of cold freshwater through them, which is not easily done.
The emergency cooling system pump and motor for a boiling-water reactor are roughly the size and height of a compact hatchback car standing on its back bumper. The powerful system has the capacity to propel thousands of gallons of water a minute throughout a reactor pressure vessel and storage pool. But that very power can also be the systemÂs Achilles heel.
The pump and piping are designed to be kept full of water. But they tend to leak and develop alternating pockets of air and water, said Mr. Friedlander, who said he had performed maintenance on the systems many times in his career.
If the pump is turned on without venting the air and draining the water, the water from the pump would hit the alternating pockets with enough force to blow holes in the piping. Venting the air and draining the water requires a technician to reach a dozen valves, sometimes using a ladder. The water is removed through a hose to the nearest drain, usually in the floor, that leads to machinery designed to remove radiation from the water.
The process takes a full 12 hours in a reactor that is operating normally, Mr. Friedlander said. But even then, the water in the pipes tends to become radioactively contaminated because the valves that separate it from the reactor are never entirely tight.
It is likely to be an even bigger problem when the water inside the reactor is much more radioactive than usual and is under extremely high pressure, as it has been in all three reactors at the Fukushima Daiichi plant at various times since the earthquake and tsunami.
Japanese government and power company officials expressed optimism on Wednesday morning that the crisis was close to being brought under control, only to encounter two reminders in the afternoon of the unpredictable difficulties that lie ahead.
Fukushima DaiichiÂs Reactor No. 3 began belching black smoke for an hour late in the afternoon, leading its operator, Tokyo Electric Power Company, to evacuate workers. No. 3 is considered one of the most dangerous of the reactors because of its fuel  mixed oxides, or mox, which contain a mixture of uranium and plutonium and can produce a more dangerous radioactive plume if scattered by fire or explosions. The cooling system at Reactor No. 5, which was shut down at the time of the earthquake and has shown few problems since, also abruptly stopped working on Wednesday afternoon, said Hiro Hasegawa, a spokesman for Tokyo Electric.
ÂWhen we switched from the temporary pump, it automatically switched off, he said. ÂWeÂll try again with a new pump in the morning.Â
This is a long way from being over. Unfortunately. :-(
Naturally, Mr. Page's latest missive (from Tuesday) continues to put the best possible spin on events there - http://www.theregist...ushima_tuesday_2/ ...
Cheers,
Scott.